Petrogenesis of the Ridge Subduction-Related Granitoids from the Taitao Peninsula, Chile Triple Junction Area

Geochemical Journal, Vol. 47, pp. 167 to 183, 2013

Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area

YOSHIAKI KON,1* TSUYOSHI KOMIYA,2 RYO ANMA,3 TAKAFUMI HIRATA,4 TAKAZO SHIBUYA,5 SHINJI YAMAMOTO2 and SHIGENORI MARUYAMA6

1Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8567, Japan 2Department of Earth Science and Astronomy, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan 3Graduate School of Life and Environmental Sciences, University of Tsukuba, Ten-no dai 1-1-1, Tsukuba 305-8572, Japan 4Laboratory for Planetary Sciences, Kyoto University, Kitashirakawa Oiwake-cho, Kyoto 606-8502, Japan 5Precambrian Ecosystem Laboratory (PEL), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka 237-0061, Japan 6Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan

(Received February 17, 2012; Accepted February 5, 2013)

Geochemical compositions are reported for Late Miocene to Pliocene granitoids from the Taitao Peninsula near the Chile ridge subduction zone. Major element compositions of Taitao granitoids show a resemblance with those of TTG suites. However, trace element compositions are characterized by low Sr (50–300 ppm), moderately high Y (10–45 ppm) and Yb concentrations (1–5 ppm), and low Sr/Y and La/Yb ratios compared with those of typical adakites, which are presumably produced by melting of young and hot oceanic crust under eclogite to garnet amphibolite conditions. Instead, trace element composition of the Taitao granitoids resembles that of typical calc–alkaline arc magmas. Based on trace element compositions, together with tectonic constraints, we infer that the Taitao granitoids were generated by partial melting of the subducted oceanic crust in garnet-free amphibolite conditions at depths shallower than 30 km. Our results indicate that slab-melting-related magmas do not necessarily show a HREE-depleted signature, which was used as evidence for slab-melting for granitic rocks of the TTG suites.

Keywords: granite, ridge-subduction, slab-melting, Taitao, adakite, TTG

subducted oceanic crust or lower mafic continental crust INTRODUCTION at garnet amphibolite to eclogite conditions (e.g., Mar- Granitoids, major constituents of the continental crust, tin, 1994, Foley, 2008). In contrast, modern granitoids, can be a major geochemical reservoir in the Earth. Un- which do not show strong HREE depletion, are regarded derstanding processes related to granitoid formation is as derived from partial melting of the metasomatized necessary to elucidate Earth’s chemical evolution. The mantle wedge (e.g., Futa and Stern, 1988; Rogers and granitoid production process might have changed during Hawkesworth, 1989) or melting of garnet-free lower mafic the Earth’s history and thereby produced chemically dif- continental crust (e.g., Nakajima and Arima, 1998). ferent granitoids. In fact, Archean tonalite–trondhjemite– Even in the Phanerozoic, some andesites and dacites granodiorite (TTG) have lower K2O contents and higher have shown chemical compositions resembling that of the La/Yb ratios because of enrichment in light rare earth el- Archean TTG (e.g., Defant and Drummond, 1990). So- ements (LREE) and depletion in heavy REE (HREE) com- called adakites, which are typically produced in hot sub- pared to modern granitoids (e.g., Barker and Arth, 1976; duction zones, are regarded as products attributable to Martin et al., 1983, Martin, 1994). These chemical dif- the partial melting of young oceanic crust (e.g., ferences are frequently explained by different melting Drummond and Defant, 1990). Furthermore, previous conditions: Archean TTG was derived from partial melt- works have emphasized that young (<20 My) plate sub- ing of a garnet-bearing basaltic material, such as duction must have caused slab melting and produced HREE-depleted magma similar to the Archean TTG, call- ing attention to the importance of hot plate subduction *Corresponding author (e-mail: [email protected]) (e.g., Peacock et al., 1994; Drummond et al., 1996; Mar- Copyright © 2013 by The Geochemical Society of Japan. tin, 1999; Prouteau et al., 1999).

167 Because the ridge subduction which accompanies South Continental shelf (< 200 m) young-plate subduction has occurred frequently during America Earth’s history, its tectonic effects on the continental margin have long been discussed using geological records, NNazcaazca plateplate particularly for the SW Japan arc (e.g., Uyeda and 9 cm/yr

Miyashiro, 1974; Isozaki, 1996, Iwamori, 2000). As for a c i the SW Japanese arc, intermittent oceanward propagation r of the granite belt appears to have occurred when mid- 6 Ma 3 Ma Present e m A oceanic ridges episodically collided and subducted be-

7 cm/yr h neath the proto-Japan arc, suggesting that the formation t u Z of granite belt is associated with ridge subduction GF o DFZ S South America TFZ (Isozaki, 1996). TMFZ Taitao Peninsula Although ridge subduction might have played an im- portant role in the origin of granitoids, the whole extent of geochemical variation of such granitoids remains un- AAntarcticntarctic plateplate 2 cm/yr constrained because of poorly defined criteria for ancient ridge subduction and related granitoids. This paper presents the chemical composition of Taitao granitoids in southern Chile, where very recent ridge subduction Fig. 1. Schematic map of South Chile showing the triple junc- occurred approximately 3 Ma and 6 Ma ago. Because the tion between the Nazca, Antarctic and South American plates. Taitao Peninsula experienced subduction of several ridges, Open triangles denote active volcanoes. it is proposed that granitic magmatism in this area is closely related to the ridge subduction that might be equivalent to an Archean subduction zone environment. Therefore, the Taitao granitoids are useful to elucidate ward from the trench axis, indicating that the top of the ridge-subduction related magmatism. slab underlying this area at present is approximately 10 Despite its importance, the origin of the Taitao km deep at maximum. granitoids remains unclear. Its chemical variation is poorly Three main geological units are present in this region: constrained. This study was conducted to elucidate the The Taitao ophiolite, a Pliocene volcaniclastic sedimen- as-yet ambiguous geochemical characteristics of the tary sequence of the Chile Margin Unit (CMU) and the Taitao granitoids to clarify the melting conditions of their Taitao granitoids. The Taitao granitoids comprise four parent magma(s) associated with ridge subduction. granitic plutons (Fig. 2a): Cabo Raper (CR), Seno Hoppner (SH), Estero Cono (EC), and Tres Montes (TM) plutons. In addition, minor dike-like intrusion of a gra- PREVIOUS WORKS OF TAITAO GRANITOIDS nitic rock is distributed in Bahia Barrientos (BB). A sum- Geological setting mary of the geochronological features of the Taitao The Chile triple junction (CTJ) is a unique geologic granitoids is presented in Fig. 2a. location where an active spreading center is colliding with Recent U–Pb dating of zircons show 3.84–3.97, 5.09– and subducting beneath an active continental margin, 5.17, 5.12, 4.88 and 5.70 Ma for granitoids from Cabo thereby forming a ridge–trench–trench configuration (Fig. Raper, Seno Hoppner, Estero Cono, Bahia Barrientos, and 1; Cande et al., 1987; Guivel et al., 1999). To the north Tres Montes granitoids, respectively (Hervé et al., 2003; of the junction, the Nazca Plate is subducting beneath the Anma et al., 2009). Anma et al. (2009) and Anma and South American Plate at a rate of 8–9 cm/year. To the Orihashi (2013) concluded using U–Pb age distributions south, the Antarctic Plate is subducting at 2 cm/year (Fig. of granitoids and sediments that the intrusion Taitao 1). The Taitao Peninsula is the westernmost promontory granitoids were all related to the ridge collision at 6 Ma of the Chilean coast and a Late Miocene ophiolite is ex- (Cande et al., 1987), subsequent subducted ridge down- posed at its western tip, approximately 50 km south of ward and the emplacement of the Taitao ophiolite. the present-day Chile Triple Junction (CTJ) (Bourgois et al., 1996). The mid-oceanic ridge passed beneath the Geochemical composition Taitao Peninsula at 3 Ma and 6 Ma ago (Cande et al., Geochemical compositions of the Taitao granitoids 1987). In the northern part of the Chile margin triple junc- have been investigated since 1990. Nevertheless, it re- tion, the slab is descending at an angle of 12°–30° (Couch mains controversial even in its whole rock composition et al., 1981; Bangs et al., 1992; Cahill and Isacks, 1985); of major and trace elements. Kaeding et al. (1990), the the tip of the Taitao Peninsula is located <17 km land- first to report whole rock compositions of the Taitao

168 Y. Kon et al. Fig. 2. Geological map and summary of geochronological data of the Taitao Peninsula. Geological map was modified after Anma et al. (2009): CR, Cabo Raper; EC, Estero Cono; SH, Seno Hoppner; BB, Bahia Barrientos; TM, Tres Montes pluton.

Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area 169 granitoids (Cabo Raper and Seno Hoppner plutons), de- sition, as proposed by Bourgois et al. (1996). However, scribed these rocks as having calc–alkaline I-type affini- these studies do not provide a satisfactory explanation ties with granodiorite and tonalite compositions for the because their data differ from typical Post-Archean calc– Cabo Raper pluton, and S-type affinity for the Seno alkaline granitoids. Hoppner pluton. The REE compositions are characterized In an attempt to establish a geochronological frame- by an enrichment in light REE with chondrite-normal- work, Anma et al. (2009) perform major and trace ele- ized Ce/Yb ratios ([Ce/Yb]N values) of ca. 5 for the Cabo ment analyses for a few samples for each pluton. Their Raper pluton, and ca. 3.5 for the Seno Hoppner pluton. data show bimodal compositions among the Taitao Both plutons show negative Eu anomaly ([Eu/Eu*]N), granitoids. The Cabo Raper, Tres Montes, Estero Cono, suggesting that plagioclase fractionation played a crucial and Bahia Barrientos granitoids were classified to TTG role in their formation (Kaeding et al., 1990). However, in major elements, and have high Sr/Y ratio (7–16). The the Eu anomaly of the Cabo Raper pluton is much lower Seno Hoppner granitoids have granitic composition (sensu than that of the Seno Hoppner pluton, which is consistent stricto) and low Sr/Y ratio (1.3–1.5). These results are with higher content in Ca and Sr of the former. They inconsistent with those reported by Kaeding et al. (1990). ferred that the granitoids were formed through assimila- tion of basaltic magma with forearc sediment or meta- SAMPLE PREPARATION AND A NALYTICAL PROCEDURES morphic basement because the Sr and Nd isotope compositions of the granitoids (0.704353–0.704974 in 87Sr/86Sr Sample preparation ε and +1.3 to +4.7 in Nd) are shown between those of the We made geological investigations of the Taitao Pe- basalt in the Taitao ophiolite (0.702709, +9.7) and sedi- ninsula twice in 2000–2001 and 2002–2003. We obtained ment/metamorphic basement (0.715475, –8.2). These iso- over 1000 samples from the Taitao granitoids, Taitao topic compositions are explainable by 5–15% mixing of ophiolite, and sedimentary units. All analyzed samples crustal components for basaltic end-members of this re- were selected after detailed observations of rock slabs and gion (Kaeding et al., 1990). thin sections to exclude highly altered samples. We se- In contrast, Bourgois et al. (1996) reported that the lected approx. 70 samples of Taitao granitoids, and pro- Taitao granitoids can be regarded as a HREE-depleted duced glass beads for major and trace element analyses. TTG, and that its origin is slab-melting under the Glass beads for the major elements analysis were pre- amphibolite–eclogite transition. They reported that the pared by mixing 0.4 g of sample powder with 4.0 g of Cabo Raper pluton has a TTG composition that is shown lithium tetraborate (Li2B4O7) flux. This mixture was on a field of Archean TTG (TDJ field; Martin, 1994). heated to 1,200°C for 15 min in a 95% Pt-5% Au crucible Although they described that the Cabo Raper granitoid with 30 mm inner diameters, used in an automatic bead- has TTG signature, the reported compositions show a bi- sampler. Low dilution-rate glass beads for trace element modal signature on the An–Ab–Or diagram: tonalite and analyses were also prepared 1.0 g of sample powder with granodiorite. Data are shown on the K–Na–Ca diagram, 3.0 g of lithium tetraborate flux. For use of the excimer- but no plot showed data for the granodioritic samples, laser ablation method, 0.04 g of FeO powder was added which should be shown out of the TDJ field. The REE for effective laser beam absorption. content of the Cabo Raper pluton was also reported, with heavy HREE-depletion without a Eu anomaly and de- Instruments and analytical conditions of LA-ICPMS pleted isotope signatures of 0.7045 and +1.5, respectively, Major elements were analyzed using X-ray fluores- 87 86 ε in Sr/ Sr and Nd. However, their Sr content and [La/ cence (XRF) spectrometry (Symaltics 3550; Rigaku Yb]N values are lower than those of typical HREE- Corp.) at the Tokyo Institute of Technology with meth- depleted Archean TTG. ods described by Goto and Tatsumi (1994). Most sam- Guivel et al. (1999) evaluated the chemical composi- ples from the Taitao Peninsula show major element ox- tions of the Cabo Raper, Seno Hoppner and Tres Montes ides above 98 wt%. plutons, and reported that the Cabo Raper and Tres Montes Trace elements were analyzed using two types of granitoid plutons possess tonalite and granodiorite affin- laser-ablation ICP-MS (LA-ICPMS) with glass-bead ab- ity, whereas the Seno Hoppner pluton has trondhjemite– lation method to decompose the refractory minerals with granite composition. They concluded that the Seno certainty (e.g., Orihashi and Hirata, 2003; Kon et al., Hoppner pluton display characteristics of typical calc– 2011). The ICP-MS instrument used for this study was a, alkaline series, different from the Cabo Raper and Tres quadrupole-based ICP-MS (VG PlasmaQuad 2; Thermo Montes plutons. Without REE patterns of the granitoids, Elemental) equipped with an S-option interface (Hirata they also followed the interpretation that the Cabo Raper and Nesbitt, 1995, 1997; Hirata, 2000). The excimer- and Tres Montes granitoid plutons originated from slab- laser ablation system (GeoLas 200CQ; MicroLas melting under the condition of amphibolite–eclogite tran- Lasersystem GmbH, Gottingen, Germany) uses an ArF

170 Y. Kon et al. 140% 130% 120% 110% 100% 90% 80%

70% JB3 JA1 JR2

Fitness for reference values 60% Ga Rb Sr Y Zr Nb Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Th U

Fig. 3. Fitness of our trace-element analyses for the published recommended values. Results show agreement with approx. 20% relative uncertainty with the published recommended values.

excimer laser (COMPex 102; Lambda Physik, Gottingen, grained plagioclases have euhedral texture. The pluton Germany) as a 193 nm DUV (deep ultraviolet) light commonly contains amphibolite enclaves of various sizes source. The laser system was operated with a pit size of ranging from 20 cm to a few meters across. They all con- 120 um diameter, pulse energy of 140 mJ/cm2, pulse rep- tain hornblende, and their lithofacies are quite homoge- etition of 15 Hz, and 100 sec ablation. To minimize el- neous at all locations (Fig. 2b). emental fractionation during ablation and to ablate the The Seno Hoppner and Estero Cono granitoid plutons glass beads effectively, the ablation spot was moved comprise two contrasting lithofacies: hornblende (hbl)- through the analysis of 10 µm/s. Another laser-ablation bearing and hbl-free. The hbl-bearing granitoids, located system comprises a Ti:S femtosecond (fs) laser (IFRIT; in the southern part of the Estero Cono pluton (Fig. 2c), Cyber Laser Inc., Japan) with a 780 nm near infrared consist of plagioclase, alkali feldspar, quartz, biotite, and (NIR) light source. The laser system was operated with a hornblende. Ilmenite, apatite, zircon and sphene are com- pit diameter of approx. 20 µm, pulse energy 100 µJ/cm2, mon accessory phases. Rutile and pyrite occur only rarely. a pulse repetition rate 500 Hz and 120 sec ablation. Un- The hbl-free granitoids distributed throughout the entire der these conditions, the laser can create an approx. 300 area of the Seno Hoppner pluton, and the northern part of µm deep pit within 0.1 sec (Hirata and Kon, 2008). To the Estero Cono pluton consist predominantly of alkali minimize elemental fractionation during ablation and to feldspar, quartz, plagioclase and biotite. Magnetite, apa- ablate the glass beads effectively, the ablation spot was tite and zircon are common accessory phases. Ilmenite is also moved through the analysis of 50 µm/sec. less common than the hbl-bearing granitoids. Hornblende, All elemental abundances were calibrated using gran- sphene and pyrite occur sporadically. ite reference material (JG-1a) glass beads. Ca was used as an internal normalization. The abundance of trace ele- Major element compositions of Taitao granitoids ments in GSJ rock reference materials (JB-3, JA-1, and Compositions of the Cabo Raper pluton are quite ho- JR-2) was measured using each method. The results mogeneous with SiO2 ranging from 65.5–68.5 wt% (Ta- showed agreement within approx. 20% relative uncer- ble 1, Fig. 4). In a CIPW normative Ab–An–Or diagram tainty with the published recommended values (Fig. 3, (Barker, 1979) and a molar K–Na–Ca diagram (Martin, Ga and Nb of JB-3 and JR-2—Imai et al., 1995; other 1994), the rocks of the Cabo Raper pluton are shown re- elements of JB-3 and JR-2—Dulski, 2001; Zr, Nb and Hf spectively on tonalite field and the TDJ field (Figs. 5a of JA-1—Lu et al., 2007; other elements of JA-1— and 5b). They are characterized by low K/Na ratios (ca. Makishima and Nakamura, 2006). 0.5), high Al2O3 (ca. 16 wt%), extremely high Mg number [Mg# = Mg/(Mg + Fe)] (ca. 0.55), and low alumina satu- ration index [ASI = Al O /(CaO + Na O + K O)] (ca. 1.0). RESULTS 2 3 2 2 Although we analyzed more than 40 samples from the Petrography Cabo Raper pluton, no granodioritic rock was found, as Rocks of the Cabo Raper pluton consist predominantly reported by Bourgois et al. (1996). of plagioclase, quartz, biotite, hornblende, and alkali feld- The Seno Hoppner and Estero Cono granitoids have spar. Ilmenite, apatite, zircon and sphene are common compositions ranging from 65–77% in SiO2 (Fig. 4). Only accessory phases. Magnetite, rutile, and pyrite occur two float-samples from SE part of the Estero Cono rarely. The grain sizes of the major igneous minerals are (TPG237, TPG241) have low SiO2 content (61–63 wt%). about 0.2–1.5 mm across. Most hornblende and some fine- They are similar to the average adakite composition

Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area 171 elated rocks

aitao granitoids and r ++++++++++++++ + + + + 0.553.22 0.53 3.12 0.52 3.04 0.560.14 3.30 0.54 0.14 3.31 0.55 0.13 3.29 0.55 0.14 3.21 0.51 0.14 3.00 0.53 0.14 3.12 0.55 0.14 3.30 0.57 0.13 3.43 0.55 0.13 3.19 0.55 0.14 3.28 0.56 0.15 3.27 0.55 0.14 3.18 0.58 0.14 3.40 0.14 0.54 3.16 0.14 0.53 3.10 0.15 0.14 0.14 66.80 67.0716.58 67.69 16.71 67.80 16.47 66.42 16.67 67.63 16.33 67.58 16.89 68.25 16.86 67.85 16.86 67.87 16.56 67.05 16.97 67.37 16.85 67.80 16.92 67.05 16.43 16.73 67.32 16.92 66.80 16.80 67.61 16.45 67.21 16.56 TPB047 TPB048 TPB049 TPB051 TPB052 TPB053 TPB054 TPB056 TPB057 TPB058 TPB060 TPB061 TPB063 TPB065 TPB220W TPB220Y TPB225W TPB225Y 3 3 2 5 O O 4.49 4.56 4.42 4.41 4.35 4.43 4.46 4.45 4.50 4.73 4.36 4.54 4.32 4.52 4.56 4.41 4.47 4.46 2 O 2 2 O 2.19 2.03 2.18 2.16 2.23 1.98 2.13 2.00 2.09 1.91 2.05 2.17 2.07 2.06 1.91 1.93 2.26 2.19 2 O 2 2 Fe K Sample No. LocalityRock type*Hbl** TO CRMajor element (wt%) SiO TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR CR TO CR TO CR TO CR TO TiO t Al MnOMgOCaONa 0.05 1.96Total 3.79 0.05 1.86Trace element (ppm) 3.83 0.05Ga 99.77 1.81Rb 3.69Sr 0.06 99.90Y 2.01Zr 3.78 0.06 17.6 99.99Nb 2.02 83.5Ba 100.88 295.7 0.06 3.84 18.5La 2.03 83.7 15.7 99.24Ce 287.3 162.3 3.90 0.05Pr 17.0 100.90 1.95 9.3Nd 80.2 295.7 427.1 11.9 128.6 100.73Sm 3.80 0.05 17.8 23.4 298.2Eu 419.2 168.3 1.81 100.92 82.0 16.1 43.8 8.0Gd 3.85 0.05 16.7 100.61 42.2 291.0 415.6 172.8Tb 4.7 1.91 19.2 77.1 16.9 73.2Dy 8.2 101.23 3.87 308.3 0.06 3.1 421.3 164.0 17.2Ho 33.1 2.02 23.4 7.0 100.61 75.3 1.2Er 16.7 57.3 308.5 174.7 412.4 2.8 8.4 3.67Tm 0.06 17.2 100.65 3.7 21.9 0.6Yb 2.08 22.2 77.4 14.3 42.0 5.7 304.9 411.6 165.5 0.9 100.33 3.0Lu 4.02 0.05 16.8 2.9 8.4 22.6 0.7Hf 4.7 100.24 1.95 17.4 291.4 420.7 154.8 76.9 16.8 0.4 44.2Th 1.8 4.5 1.1 0.05 2.2 3.78 0.3 16.4 20.9U 100.54 3.2 7.7 313.2 380.8 171.8 1.99 0.5 19.2 72.7 1.9 15.4 4.1 39.4 0.7 3.70 1.2 0.05 4.7 0.3Laser type 0.8 18.0 100.22 290.9 387.1 3.1 167.0 17.1 0.2 1.94 15.3 2.8 8.7 4.0 69.8 17.1 33.1 0.7 1.6 3.9 8.1 0.6 100.32 3.91 301.3 443.1 143.2 19.1 fs 0.05 2.1 4.5 23.4 0.2 0.9 2.8 0.2 15.5 2.0 94.3 1.96 16.4 44.9 3.2 7.2 5.5 283.1 0.7 461.6 166.2 2.5 18.0 2.2 99.85 3.96 16.6 0.5 21.6 1.9 3.5 0.4 1.1 0.06 ex 18.1 2.8 77.3 13.4 0.3 300.7 41.0 158.3 443.3 1.7 2.9 2.12 7.7 4.7 12.3 0.7 3.4 16.8 1.7 19.9 0.5 3.97 417.7 17.6 164.4 1.8 71.5 5.0 312.5 0.4 1.0 0.05 14.5 36.9 2.7 fs 0.3 2.4 3.6 1.95 7.7 4.2 18.6 7.1 0.7 18.5 3.8 411.2 2.3 155.0 0.5 15.9 77.7 16.0 3.69 41.3 1.7 308.7 4.5 0.4 1.1 0.05 3.3 0.2 2.1 fs 3.2 7.9 4.2 25.0 17.4 401.0 1.91 6.9 0.5 1.8 4.3 16.1 170.8 13.6 0.6 44.4 65.2 293.0 3.71 1.7 4.2 0.2 0.9 2.9 0.3 21.5 2.2 405.5 3.2 4.2 8.2 5.9 0.6 18.9 fs 17.3 157.0 40.8 1.4 4.1 16.8 278.1 0.5 73.0 1.7 4.2 0.3 1.2 15.9 3.3 0.3 447.2 1.6 16.6 2.8 9.2 3.9 151.9 4.4 32.7 0.6 15.9 1.8 3.4 fs 16.8 0.6 98.4 1.8 4.8 0.3 1.0 21.6 409.7 3.1 14.8 0.3 2.2 3.0 9.3 4.1 39.2 7.6 0.7 15.7 2.1 3.7 16.7 fs 0.5 92.2 1.6 4.7 0.3 1.0 2.7 17.7 22.8 0.2 1.9 2.1 4.6 6.9 42.4 0.6 7.7 4.2 2.0 0.6 16.2 fs 1.6 3.9 0.3 0.9 2.2 23.6 0.2 20.0 1.7 2.1 4.5 5.6 44.4 0.6 3.9 1.7 9.5 0.4 1.7 0.2 1.0 fs 4.2 2.5 22.9 0.3 18.2 1.3 3.2 6.1 5.9 0.6 41.5 1.8 3.5 0.4 9.7 1.5 0.3 2.3 1.1 0.3 fs 1.9 17.7 4.8 4.6 8.5 0.6 3.0 1.6 0.5 10.3 3.7 1.7 0.2 0.3 3.1 1.7 ex 1.1 4.0 6.9 5.2 2.0 0.7 3.0 0.2 1.9 4.2 0.6 1.6 0.3 3.9 4.8 3.1 fs 0.9 4.1 1.9 0.7 3.0 0.2 1.4 0.5 4.5 1.9 4.3 0.3 5.8 fs 3.0 1.0 1.6 0.6 3.4 0.3 1.1 1.8 0.6 0.4 4.6 fs 6.8 2.5 2.3 0.7 0.3 1.2 1.9 0.2 4.2 8.4 fs 1.7 0.3 2.6 4.0 7.4 fs 2.0 fs fs P

Table 1. Major and trace element compositions of T Table

172 Y. Kon et al. .

ee granitoid (–).

rientos; TO, tonalite; TR, trondhjemite; GD, granodiorite; GR, granite; fs, femtosecond laser; ex, excimer laser tonalite; TR, trondhjemite; rientos; TO,

Ab–An–Or diagram of Barker (1979). TPE080 TPE081 TPE082 TPE083 TPE086 TPE088 TPE090 TPE091 TPE092 TPE094 TPE096 TPD168 TPD171 TPE130

e classified based on CIPW normative

o Cono; SH, Seno Hoppner; BB, Bahia Bar ++++++++++++++++++ 0.533.18 0.54 3.19 0.53 3.03 0.570.14 3.39 0.51 0.14 3.10 0.53 0.13 3.28 0.57 0.14 3.35 0.49 0.14 3.14 0.48 0.14 2.86 0.56 0.14 3.36 0.55 0.14 3.27 0.51 0.15 3.05 0.55 0.14 3.35 0.54 0.14 3.13 0.55 0.14 3.24 0.47 0.15 2.75 0.48 0.13 3.05 0.47 0.14 2.64 0.10 0.10 0.10 66.83 67.1216.40 66.53 16.64 66.43 16.26 67.20 16.60 67.00 16.81 66.59 16.78 66.23 16.70 67.87 16.70 67.01 16.96 65.48 16.56 66.51 16.54 66.68 16.42 66.84 16.78 67.37 16.58 69.28 16.77 68.30 15.79 68.66 15.90 15.67 TPB228 TPB231 TPB234 TPB238 3 3 2 5 O O 4.46 4.38 4.52 4.44 4.42 4.31 4.47 4.53 4.41 4.30 4.29 4.48 4.41 4.42 4.39 4.08 4.32 4.11 2 O 2 2 O 2.27 2.31 2.24 2.16 2.17 2.12 2.00 2.16 2.00 2.15 2.14 2.25 2.19 2.18 2.17 2.23 1.97 2.49 2 O 2 2 Fe K Al MnOMgOCaONa 0.05 2.00Total 3.60 0.05 1.93Trace element (ppm) 3.69 0.05Ga 99.47 1.89Rb 3.71Sr 0.06 99.97Y 2.04Zr 3.83 0.05 15.8 98.89Nb 1.95 82.7Ba 294.6 99.65 0.06 3.86 15.6La 2.10 81.3 16.4 100.22Ce 278.5 164.7 3.92 0.06Pr 16.5 100.24 2.11 8.0Nd 85.5 303.1 457.9 14.2 140.2Sm 3.87 0.06 99.88 15.9 26.6 301.9Eu 446.1 156.5 2.00 80.6 17.2 48.7 7.6Gd 99.42 3.97 0.05 17.5 22.7 282.6 437.0 165.6Tb 5.3 1.71 22.3 100.28 90.6 14.3 44.1Dy 8.3 3.79 309.7 0.06 3.8 435.9 141.0 17.0Ho 100.05 22.1 2.09 17.6 4.7 84.1 0.9Er 14.6 42.9 272.6 169.3 425.5 3.9 8.9 3.82Tm 98.39 0.06 19.5 3.6 24.7 0.5Yb 2.02 18.5 82.7 16.2 46.5 4.9 278.7 401.1 132.5 0.9 2.9 99.01Lu 3.90 0.05 19.1 3.0 7.7 20.5 0.6Hf 4.5 100.17 1.82 17.9 285.2 388.3 138.5 86.8 11.5 0.5 41.6Th 1.8 5.0 0.8 0.06 2.6 3.78 0.3 17.4 25.0U 99.59 3.2 9.8 283.1 358.1 128.8 2.03 0.6 17.0 93.8 1.9 15.8 3.6 47.2 0.7 100.50 3.96 1.6 0.05 4.5 0.2Laser type 1.1 16.8 290.1 398.7 3.0 139.7 21.0 0.3 1.91 20.0 2.4 8.1 4.3 83.9 13.8 44.7 0.6 1.8 3.5 99.84 8.9 0.4 3.80 278.4 434.9 0.05 136.6 16.3 fs 1.9 5.3 21.1 0.3 1.0 2.2 0.3 1.96 15.4 1.6 75.4 13.6 44.5 99.46 3.2 7.9 5.9 287.4 0.7 443.4 133.3 3.6 1.9 3.87 0.05 8.4 16.8 0.5 20.3 1.7 4.3 0.2 1.2 ex 1.58 98.88 18.1 2.8 86.6 13.6 0.3 280.6 41.1 140.8 387.2 1.0 2.6 8.0 3.9 0.6 3.51 0.05 3.0 17.1 2.2 20.8 7.1 0.5 284.3 433.4 1.72 15.8 134.4 1.6 81.9 4.8 0.3 0.9 15.5 41.3 3.4 fs 0.2 0.9 2.6 3.58 0.03 7.9 4.6 18.0 0.8 19.2 3.8 161.6 401.7 1.8 133.3 8.1 0.4 1.44 16.2 81.2 15.2 39.7 1.7 4.2 0.2 1.0 2.2 0.3 3.28 2.2 17.8 167.4 436.7 fs 136.8 3.1 7.8 4.7 20.4 0.5 1.7 3.1 16.1 81.6 13.3 7.4 0.6 41.6 1.3 4.3 0.3 147.4 0.9 484.2 148.5 3.1 14.4 0.2 18.7 1.2 2.8 4.8 8.3 ex 0.7 16.7 72.9 12.5 38.8 1.4 3.3 7.8 508.9 139.2 0.5 1.8 4.2 0.2 16.0 0.9 22.7 2.4 0.3 2.0 16.9 2.8 7.9 5.9 64.6 16.0 45.1 467.4 0.6 fs 2.0 3.4 8.0 0.5 14.9 1.5 19.1 4.4 0.3 0.9 100.4 2.5 17.1 0.2 1.4 17.7 40.2 3.0 7.7 6.2 0.6 1.9 3.4 ex 7.4 0.5 14.5 1.5 4.3 0.3 15.6 0.9 2.5 15.5 31.2 0.2 1.1 3.0 7.9 7.8 0.6 3.6 1.7 16.4 ex 7.6 0.5 13.5 1.5 4.7 0.2 1.0 36.6 2.8 0.2 1.1 3.1 5.6 5.2 0.6 17.4 3.4 1.8 15.4 6.7 0.5 ex 37.3 1.7 4.2 0.2 0.9 3.0 0.3 1.0 2.9 6.0 6.6 0.6 14.7 3.2 1.9 6.2 0.5 1.7 ex 3.4 0.3 0.9 2.5 0.3 1.3 2.8 5.4 5.7 0.6 1.8 3.1 7.3 0.4 1.5 4.0 0.3 ex 0.7 2.4 0.2 1.7 2.8 6.7 0.5 1.7 3.6 5.8 0.5 1.6 3.9 0.2 0.7 ex 2.9 0.2 1.2 3.3 5.3 0.6 1.6 3.1 8.4 0.6 1.8 0.2 0.7 3.2 ex 0.3 1.8 2.9 5.5 0.7 1.9 6.3 0.5 2.0 0.3 2.7 0.3 1.3 ex 6.0 0.6 2.4 6.9 1.7 0.3 0.2 1.9 ex 6.3 1.8 7.1 0.3 2.7 5.8 ex 7.1 2.3 ex ex TiO t Sample No. LocalityRock type*Hbl** TO CRMajor element (wt%) SiO GD CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR TO CR GD EC TO EC GD EC P

*Rock types of granitoid wer **Presence or absence of hornblende was described: Hbl-bearing granitoid (+), Hbl-fr **Presence CR, Cabo Raper; EC, Ester

Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area 173 + −−−−−−− +++++ + ++ 0.502.85 0.58 3.50 0.49 2.89 0.520.10 3.11 0.49 0.15 2.65 0.54 0.10 2.64 0.41 0.10 2.43 0.44 0.10 2.24 0.44 0.10 2.31 0.39 0.09 2.35 0.17 0.09 1.42 0.23 0.09 1.62 0.20 0.09 0.84 0.28 0.05 2.63 0.19 0.05 0.62 0.18 0.05 1.48 0.18 0.06 1.51 0.36 0.04 2.33 0.04 0.04 0.10 69.7116.23 67.93 16.93 69.40 69.11 16.32 70.02 16.23 68.76 15.85 72.13 16.59 15.70 70.23 15.97 68.75 16.36 70.83 76.93 15.37 74.55 14.04 75.39 14.84 72.30 14.44 77.37 15.09 75.86 14.29 75.21 13.85 69.23 13.72 16.96 3 3 2 5 O O 4.27 4.51 4.18 4.17 4.08 4.99 4.55 4.86 4.96 4.15 4.45 4.67 4.95 4.76 5.55 4.59 4.57 4.82 2 O 2 2 O 2.22 2.01 2.02 1.84 2.48 1.10 2.31 1.59 1.67 2.57 3.10 2.57 2.64 1.91 0.21 3.04 3.16 1.46 2 O 2 2 Fe K Sample No.Locality TPE135Rock type* TPE135YHbl** TPE136 TO EC TPE138 TPE139SiO TPE152 TO EC + TPE158 TPE159W TPE159Y TO EC TPE160 + TPE384 TO EC TPE387 TPE388 TPE390 GD EC TPE397 TPG213 TO EC TPG216 TPG236 GD EC TO EC TO EC GD EC GR EC TR EC TR EC TR EC TR EC GR EC GR EC TO EC Major element (wt%) P Al MnOMgOCaONa 0.04 1.55Total 3.50 0.06 2.10Trace element (ppm) 3.86Ga 0.03 100.96Rb 1.48Sr 101.63 3.56 0.04Y 1.72 100.47Zr 13.9 3.50 0.03Nb 100.35 89.1 1.36Ba 169.3 100.03 2.98La 0.03 17.3 22.4Ce 1.56 75.0 100.10 191.9 303.7Pr 3.78 0.03 16.1 101.60 6.8Nd 437.4 1.08 15.5 188.8 84.9 154.3Sm 100.03 2.86 21.4 17.5 0.01Eu 420.2 163.3 149.8 41.4 64.4 1.23 8.3 18.4Gd 99.34Tb 3.37 17.5 4.9 20.6 137.7 447.0 170.1 17.1 104.6 0.02Dy 38.2 20.3 5.8 1.24 3.4 99.88Ho 212.9 429.0 152.7 19.0 22.6 0.8 3.51 49.6Er 16.0 4.1 0.04 101.38 18.5 49.1 3.5Tm 139.3 467.4 1.23 193.2 6.7 14.6 3.0 20.8 100.37 0.7Yb 94.9 2.86 0.02 18.9 19.1 43.5 4.5 5.0 1.0Lu 375.1 180.4 201.8 0.07 99.93 0.9 2.2Hf 6.7 19.0 15.4 3.9 1.13 0.02 19.2 59.0 0.5 503.5Th 18.1 2.5 41.9 182.4 4.9 99.47 0.5 202.8 0.8 0.12 2.8U 21.5 3.6 7.3 3.1 0.6 1.68 486.3 0.01 17.1 16.2 100.73 4.2 51.5 17.4 184.3 64.2 138.4 0.6 0.4Laser type 0.06 1.4 4.5 0.9 100.39 3.4 0.3 21.9 5.1 0.02 1.36 4.0 20.0 6.1 16.1 503.1 0.8 143.2 108.6 44.7 1.5 9.0 3.9 85.3 0.33 fs 0.7 17.0 99.61 2.0 0.3 5.3 0.8 2.4 20.8 3.8 2.08 0.3 494.0 0.00 181.0 108.6 17.7 17.8 116.0 4.6 100.26 3.5 44.0 0.8 6.6 0.19 2.2 4.1 18.9 5.9 0.6 756.0 176.7 2.5 4.7 fs 0.3 2.25 138.9 0.8 0.02 94.0 3.1 18.7 17.8 17.2 0.3 1.4 3.8 5.8 0.08 0.8 37.8 30.4 962.8 2.6 3.6 209.6 150.1 6.7 8.1 0.6 1.23 0.02 85.8 2.1 15.1 0.4 0.7 20.9 4.7 3.5 0.3 ex 1115.8 2.4 15.6 0.03 194.3 3.3 22.1 6.7 237.8 43.1 0.8 2.3 3.6 1.18 62.1 8.9 0.04 6.6 0.6 17.8 776.2 21.5 2.3 200.5 0.3 0.8 1.43 3.2 17.2 0.3 2.6 26.4 88.4 51.4 ex 4.1 6.9 3.5 0.7 215.8 3.51 2.3 14.3 193.5 5.6 8.5 7.7 15.0 0.6 3.4 2.1 21.9 0.4 22.3 69.9 36.5 0.3 3.1 647.8 2.8 4.7 0.8 ex 193.7 7.2 110.1 13.9 0.7 2.5 19.6 3.2 8.0 7.9 256.1 15.5 33.6 544.5 3.8 41.3 0.3 2.0 0.5 120.7 2.4 94.9 0.3 5.5 15.3 0.7 6.7 3.0 14.1 ex 244.4 2.2 18.4 3.4 9.8 7.3 30.5 31.4 0.7 5.2 46.5 0.3 0.6 12.5 2.4 1.8 24.4 3.9 0.5 3.2 8.1 0.3 14.4 ex 32.0 53.0 5.2 7.8 8.3 0.8 2.2 3.9 0.9 28.4 2.2 0.3 2.4 4.7 25.3 0.6 5.4 57.9 0.3 8.1 ex 6.8 4.0 8.0 1.3 2.5 4.2 27.1 8.3 0.6 24.9 3.4 3.5 0.3 54.4 0.6 3.8 0.5 2.4 4.6 7.9 7.9 0.9 10.7 3.6 10.7 3.6 ex 24.0 0.8 20.8 2.4 6.2 0.5 0.8 4.6 0.4 3.2 3.8 7.6 9.6 13.2 1.1 6.2 3.0 9.3 0.7 ex 3.1 6.7 0.4 0.6 3.8 0.5 4.3 5.8 3.1 8.2 9.7 0.9 5.3 3.2 1.1 ex 2.4 6.3 0.5 0.8 6.0 0.4 3.4 11.1 11.7 4.8 1.4 3.0 5.8 0.9 3.8 ex 2.5 0.4 0.6 5.6 0.6 9.4 3.1 9.6 5.0 1.1 4.3 2.0 0.9 3.5 0.6 0.6 ex 6.1 13.5 0.5 3.0 8.3 1.8 1.2 3.9 0.3 3.7 0.5 11.3 ex 2.0 0.6 3.8 6.2 0.3 4.0 12.7 0.9 0.6 0.1 ex 3.1 6.5 0.9 3.4 0.1 3.3 2.7 fs 1.3 fs fs TiO t

Table 1. (continued) Table

174 Y. Kon et al. . ornfels basement basement hornfels hornfels −−−−

– +

ee granitoid ( −

Or diagram of Barker (1979).

–

rientos; TO, tonalite; TR, trondhjemite; GD, granodiorite; GR, granite; fs, femtosecond laser; ex, excimer laser tonalite; TR, trondhjemite; rientos; TO,

–

Ab ++ −

e classified based on CIPW normative

o Cono; SH, Seno Hoppner; BB, Bahia Bar 0.844.52 0.40 2.50 1.11 5.70 0.220.19 2.19 0.24 0.12 2.32 0.53 0.24 3.46 0.18 0.06 1.33 0.23 0.06 2.19 0.51 0.11 3.40 0.26 0.05 2.23 0.22 0.06 2.12 0.25 0.11 2.07 0.22 0.06 2.20 0.67 0.05 6.07 0.48 0.07 3.01 0.58 0.06 4.15 0.95 0.18 7.00 0.83 0.12 5.10 0.14 0.22 0.22 63.23 69.1316.60 60.85 16.71 74.84 17.20 75.69 13.89 67.21 14.28 76.04 16.41 75.55 13.77 66.66 14.04 74.69 16.65 74.95 13.99 74.04 14.00 74.31 14.04 51.03 13.85 15.83 73.38 13.31 70.72 61.24 14.31 68.46 18.62 14.96 3 3 2 5 O O 4.75 4.87 4.46 4.96 5.12 4.25 4.62 4.79 3.91 4.86 4.86 5.00 4.97 1.04 3.51 3.24 3.39 3.02 2 O 2 2 O 1.54 1.19 1.49 3.03 2.86 2.16 2.91 3.15 2.03 3.00 3.13 3.03 3.06 1.26 2.60 2.39 2.39 2.15 2 O 2 2 Fe K Hbl**++++ Major element (wt%) Sample No.Locality TPG237Rock type* TPG239 TPG241 TO EC TPD103 TPD104SiO TPD106 TO EC TPD107 TPD108 diorite TPD109 EC TPD110 TR TPD114 TPD116 SH TPD172 TR TPE131 SH TPE133 TO TPE366 SH TPE391 GR TPG238 SH GR SH TO SH GR SH GR SH TR SH GR SH h EC EC EC EC EC TiO t Al MnOMgOCaONa 0.07 2.47Total 4.71 0.04 1.46Trace element (ppm) 3.67 0.10Ga 98.92 2.79Rb 5.21Sr 0.03 100.09Y 0.15Zr 99.15 1.15 0.03 15.9Nb 0.17 68.9 100.52Ba 204.2 0.05 1.22 17.7La 102.00 1.83 40.1 24.0Ce 319.7 161.0 3.76 0.01 99.78Pr 19.1 0.02 9.8Nd 76.7 213.1 381.7 124.5 100.18 9.7Sm 1.24 0.03 15.0 22.5 101.33 119.9Eu 351.1 145.0 0.19 53.0 45.7 3.7 24.1Gd 1.11 0.05 16.4 99.79 15.4 112.1 330.7 240.7Tb 5.3 2.27 20.9 61.6 31.9 11.6Dy 34.9 100.58 4.21 0.03 4.7 505.2 259.2 16.8Ho 82.2 20.9 187.3 0.23 13.3 3.4 100.56 1.2Er 46.4 35.8 8.6 212.0 533.3 4.3 1.22 102.7Tm 0.03 14.4 2.8 29.1 99.91 86.5 0.7Yb 0.12 21.0 56.5 5.3 395.5 214.9 0.8 22.6 4.4 125.1Lu 7.9 1.08 0.03 16.2 99.88 2.3 31.2 1.0Hf 53.6 4.8 0.15 27.6 766.0 243.3 0.4 62.3 32.2Th 2.7 96.0 6.9 1.3 99.07 0.03 1.8 1.23 0.4 17.5 6.3 20.7 232.6U 4.9 480.2 179.8 0.01 0.4 28.0 2.9 5.8 42.9 144.8 34.3 0.8 99.43 1.15 1.1 0.20 6.9 0.4Laser type 0.8 17.2 432.1 4.5 214.3 33.6 51.9 0.2 7.7 2.89 18.3 6.8 5.7 156.7 65.9 1.0 1.2 21.8 6.7 19.90 99.03 8.0 1.1 492.7 234.6 ex 14.8 0.04 2.6 5.2 26.4 59.4 0.2 1.0 132.4 5.8 0.4 27.9 2.1 8.7 1.34 54.9 5.7 4.4 99.13 37.5 1.5 492.3 241.3 3.7 3.1 1.65 5.4 155.7 15.5 1.1 23.2 54.6 0.08 4.5 7.4 ex 0.4 0.9 24.4 98.90 6.4 0.7 46.9 228.2 479.0 1.7 7.1 1.45 35.8 4.2 5.0 1.3 6.1 1.98 19.1 4.9 32.4 45.6 27.1 5.5 0.7 0.10 462.2 22.1 4.0 5.8 0.6 0.6 60.1 ex 87.8 3.7 2.47 41.2 0.5 1.8 9.1 4.3 414.2 7.0 2.74 103.6 17.2 0.9 36.3 0.05 6.1 13.0 921.5 4.4 0.9 28.3 200.3 71.6 3.0 1.65 5.5 37.1 0.7 0.9 6.0 0.3 fs 162.8 3.3 9.4 2.46 6.0 7.0 46.9 83.5 16.8 436.7 10.8 1.3 2.9 4.7 31.5 134.9 0.9 97.1 18.3 3.7 6.9 0.4 227.4 1.1 6.5 104.5 0.5 27.7 602.1 2.6 8.4 fs 4.0 4.6 17.8 166.2 7.9 1.4 45.7 60.1 3.7 6.8 250.4 0.6 109.6 20.3 4.0 563.8 8.0 0.6 0.9 272.5 22.4 4.2 0.6 1.7 9.7 23.6 12.9 26.3 7.2 7.2 217.4 49.3 fs 1.0 4.5 6.7 402.8 1.3 18.1 11.4 2.2 0.7 0.9 32.2 16.4 7.0 11.3 21.0 0.3 3.2 6.4 5.6 6.6 67.0 10.9 1.5 2.3 fs 25.1 1.0 6.7 4.2 0.5 22.3 1.0 6.3 27.0 8.7 0.7 3.1 10.6 8.0 50.9 5.4 6.2 35.2 1.5 4.8 fs 1.7 5.4 30.1 4.0 12.5 0.7 0.8 20.6 8.4 0.6 6.1 66.1 2.3 9.8 4.4 8.8 1.9 4.0 50.6 1.1 11.8 7.2 fs 29.6 4.8 0.8 1.1 86.5 6.4 0.7 3.8 2.7 11.5 6.6 1.4 5.2 4.7 12.5 0.6 42.9 4.1 0.6 5.4 ex 3.4 1.1 15.2 0.7 3.3 4.4 6.4 0.7 13.6 4.9 4.4 0.7 2.0 0.7 7.5 0.3 fs 3.8 11.2 1.1 2.5 3.7 6.4 2.4 0.9 6.3 10.9 0.3 0.6 2.3 3.3 3.1 1.3 0.3 3.5 fs 5.4 8.1 9.8 2.5 0.7 0.9 0.4 2.0 1.9 1.4 4.7 8.4 0.3 6.8 ex 1.1 7.5 2.5 1.1 3.1 0.4 6.3 2.2 0.4 5.5 ex 10.8 1.4 3.3 3.8 0.5 0.6 14.5 1.9 5.0 ex 4.1 0.6 10.2 2.6 ex 3.1 ex ex P

**Presence or absence of hornblende was described: Hbl-bearing granitoid (+), Hbl-fr **Presence CR, Cabo Raper; EC, Ester

*Rock types of granitoid wer

Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area 175 1.5 20 0.15 TiO2 18 Al2O3 MnO 1 16 0.10 0.5 14 0.05 12 0 10 0.00 8 6 8 FeOt MgO CaO 6 6 4 4 4 2 2 2 0 0 0 10 8 0.3 Na2O K2O P2O5 8 6 6 0.2 4 4 0.1 2 2 0 0 0 0.8 2 60 70 80 Mg# K/Na SiO2 0.6 1.5 This study hbl-bearing hbl-free 0.4 1 Cabo Raper 0.2 0.5 Seno Hoppner 0 0 Estero Cono 60 70 80 60 70 80 SiO2 SiO2 Compilation data Archean TTG Calc–alkaline rock (sensu stricto) Average adakite (Shimoda, 2009)

Fig. 4. Major element contents against SiO2 variation of Taitao granitoids. Compositions of Archean TTG, sensu-stricto calc– alkaline rocks and averaged adakite are also shown (references in text).

(Shimoda, 2009). Compositions of the Seno Hoppner and With increasing SiO2 contents, K/Na ratios of the hbl- Estero Cono granitoid plutons are overlapped (Fig. 4). bearing and hbl-free granitoids increase within each group Both are markedly heterogeneous, and are classified into (Figs. 4 and 5b). Compared with calc–alkaline granite and lithofacies hbl-bearing granitoids and hbl-free granitoids. rhyolite (Crecraft et al., 1981; Norman et al., 1992; Gerber The hbl-bearing granitoids are characterized by lower et al., 1995; Miller and Hoisch, 1995; Petford and SiO2 (<72.1 wt%), higher MgO (>1 wt%), and extremely Atherton, 1996; Kawano et al., 1997; Shinjoe, 1997; higher Mg# (>1.0) than that of hbl-free rocks. In con- Anma et al., 1998; Parada et al., 1999; Halla, 2005; trast, the hbl-free granitoids rocks have a high SiO2 (>72.1 Masberg et al., 2005; Shinjoe et al., 2007), the Taitao wt%), low MgO (<0.3 wt%), and Mg# (<0.3). Both hbl- granitoids have high Al2O3, MgO and Na2O contents, and bearing and hbl-free rocks have moderately low K/Na low FeO* and K2O contents and K/Na ratio (Fig. 4). The ratios (<0.8) and low ASI (<1.1). The hbl-bearing major element compositions of the Taitao granitoids granitoids are plotted in the tonalite–granodiorite field clearly possess some characteristics TTG suites (Arth et on the normative Ab–An–Or diagram, whereas hbl-free al., 1978; Bickle et al., 1983; Nutman et al., 1986; Mar- granitoids are plotted in the trondhjemite–granite field tin, 1987; Bickle et al., 1993; Kleinhanns et al., 2003; (Fig. 5a). Both are plotted on the TDJ field on a K–Na– Whalen et al., 2004; Clemens et al., 2006). Ca diagram (Fig. 5b).

176 Y. Kon et al. (a) CIPW normative An (b) K–Na–Ca diagram K Ab–An–Or diagram from Barker and Arth from Barker (1979) (1976)

CA Or TO GD

TR TDJ

G Ab Or Na Ca

Bourgois et al. (1996) Guivel et al. (1999) This study hbl-bearing hbl-free Cabo Raper Cabo Raper Cabo Raper

Kaeding et al. (1990) Seno Hoppner Seno Hoppner Cabo Raper and Seno Hoppner Estero Cono

Average adakite compositions (Shimoda, 2009)

Fig. 5. Whole rock compositions of the Taitao granitoids: (a) CIPW normative Ab–An–Or diagram from Barker (1979). An, anorthite; Ab, albite; Or, orthoclase; TO, tonalite; TR, trondhjemite; GD, granodiorite; G, granite. (b) K–Na–Ca diagram from Barker and Arth (1976). TDJ, trondhjemitic trend; CA, calc–alkaline trend. Dark shaded area is TDJ field from Martin (1994).

Trace element compositions of Taitao granitoids ized REE patterns are characterized by moderately low The trace element compositions of the Cabo Raper [La/Yb]N values (1 < [La/Yb]N < 9). granitoid are homogeneous (Fig. 6). They have a low Sr The Estero Cono granitoids show variable trace ele- (270–300 ppm), moderately high Y (12–17 ppm) and Yb ment compositions suggesting a crystal differentiation. (1.3–2.0 ppm) contents. Consequently, they possess low Most samples have low Sr (100–300 ppm) contents, mod- Sr/Y ratios (16 < Sr/Y < 25). Chondrite-normalized Eu erately high Y (10–30 ppm) and Yb (5–25 ppm) contents anomaly (chondrite values: Anders and Ebihara, 1982) is and low Sr/Y ratios (16 < Sr/Y < 25). Furthermore, Y, Ba, not readily apparent, and their [Eu/Eu*]N values are 0.9– REEs, Th, and U have positive correlation with SiO2 con- 1.2. They show slightly LREE-enriched REE patterns and tent. Sr and Eu have negative correlation with SiO2 con- have moderately low [La/Yb]N values (7 < [La/Yb]N < tent. Their [La/Yb]N and [Eu/Eu*]N values also have a 10). Only one sample (TPB048), having high LREE con- negative correlation with SiO2 content. Chondrite-normal- tents, is characterized by high [La/Yb]N values (ca. 18.5). ized REE patterns are characterized by moderately low The Seno Hoppner granitoid shows variable trace el- [La/Yb]N values (4 < [La/Yb]N < 10). Float samples from ement compositions (Fig. 6). In fact, Y, Ba, REEs, Th, SE part of the Estero Cono (TPG236, 239) have different and U have positive correlations with SiO2 content but compositions from those of other Estero Cono granitoids. Sr and Eu show a negative correlation. Their [La/Yb]N They have similar content to the other hbl-bearing and [Eu/Eu*]N values also have negative correlation with granitoids in major elements, but are characterized by low SiO2 content. They contain low Sr (100–300 ppm), mod- Y (8–10 ppm) and Yb (1–1.2 ppm) contents. They have erately high Y (10–45 ppm) and Yb (5–35 ppm) contents no Eu anomaly (0.8–1), high Sr/Y ratios (33–35) and [La/ and low Sr/Y ratios (1 < Sr/Y < 20). Chondrite-normal- Yb]N values (8–9).

Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area 177 300 1000 60 250 Rb 800 Sr Y 200 600 40 150 100 400 20 50 200 0 0 0 500 20 1500 Zr Nb Ba 400 15 300 1000 10 200 500 100 5 0 0 0 100 4 10 La Eu Yb 75 3 8 6 50 2 4 25 1 2 0 0 0 200 100 60 70 80 Sr/Y [La/Yb]N SiO2 150 75 This study hbl-bearing hbl-free 100 50 Cabo Raper 50 25 Seno Hoppner 0 0 Estero Cono 60 70 80 60 70 80 SiO2 SiO2 Compilation data Archean TTG Calc–alkaline rock (sensu stricto) Average adakite (Shimoda, 2009)

Fig. 6. Trace element contents (ppm) and ratios against SiO2 variation of Taitao granitoids. Compositions of Archean TTG, sensu-stricto calc–alkaline rocks and averaged adakite are also shown (references in text).

1996). The reported HREE depletion can be explained DISCUSSION by a false decomposition of refractory minerals such as Geochemical compositions of ridge-subduction related zircon. Our result clearly suggests that the Taitao granitoids granitoids have TTG compositions in major elements, but The origin of the Taitao granitoids is spatially and tem- no significant HREE-depletion was recognized, which is porally related to the subduction of a spreading center of comparable to Archean TTGs and adakites. the Chile ridge system that started at the latitude of Taitao Peninsula of ca. 6 Ma ago, and to the subsequent em- Possible source rock of the Taitao granitoids placement of the Taitao ophiolite (Anma et al., 2009) It has been pointed out that possible source materials granitoids. of granitic magmas in the hot subduction zones are de- We analyzed more than 40 samples collected from rived from subducted MORB (Kay, 1978; Defant and various localities in the Cabo Raper pluton (Fig. 2b). Our Drummond, 1990), subducted sediments (Shimoda et al., results show very homogeneous geochemical composi- 1998, 2003; Shimoda and Tatsumi, 1999), accretionary tions even in HREE content (Figs. 6 and 7), in contrast to prism (Shinjoe, 1997), and/or mantle peridotites previously reported geochemical variations and HREE (Kelemen, 1995). depletions of the Cabo Raper granitoid (Bourgois et al., The Taitao Peninsula is located near a subduction zone

178 Y. Kon et al. 1000 (a) Cabo Raper (hbl-bearing) (b) Previous works

100

Chondrite Normalized 1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1000 (c) Estero Cono (hbl-bearing) (d) Estero Cono (hbl-free)

100

Chondrite Normalized 1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1000 (e) Seno Hoppner (hbl-bearing) (f) Seno Hoppner (hbl-free)

100

Chondrite Normalized 1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Archean TTG Taitao granitoids (This study) Post-Archean Kaeding et al., 1990 (CR, SH) calc–alkaline granitoids Bourgois et al., 1996 (CR)

Fig. 7. Chondrite normalized REE patterns of the Taitao granitoids: (a) Cabo Raper hbl-bearing, (b) previously reported, (c) Seno Hoppner hbl-bearing, (d) Seno Hoppner hbl-free, (e) Estero Cono hbl-bearing, and (f) Estero Cono hbl-free granitoid.

Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area 179 (a) Sr/Y eclogite hbl- hbl- Geochemical constraints on depth of melting melting Taitai granitoids bearing free 500 Cabo Raper Mineral paragenesis of the basaltic source rock con- Seno Hoppner trols the trace element compositions of the granitic melts. 10% Garnet Estero Cono 400 If a basaltic source rock contains abundant plagioclase, amphibolite Crustal components melting This study then the generated magma is enriched in Y and Yb, and Kaeding et al. (1990) 300 has low [La/Yb]N and Sr/Y ratios, compared with magma formed in the garnet stability field. Figure 8 shows [La/ 10 Yb] vs. [Yb] and Sr/Y vs. Y diagrams (Martin, 1986; 200 Adakite N N Drummond and Defant, 1990), and enables us to estimate the melting pressure of the basaltic source rock (Fig. 8). 100 30 50 Island Arc ADR Sedimentary rocks of the Taitao Peninsula have simi- Y 0 lar contents to the Taitao granitoids in the trace element (Fig. 8), which suggests that the trace element composi- (b) 0 1020304050 tion does not change by crustal contamination. (La/Yb)N eclogite The low Y and Yb contents of the Taitao granitoids 150 might indicate that they were generated by more than 50% 25% Garnet of the partial melting of a basaltic source rock in the amphibolite melting garnet-stability field (Fig. 8). However, such a high de- gree of melting is not reasonable to generate a granitic 100 TTG magma. An alternative explanation of the trace element 10% Garnet compositions is partial melting of amphibolite under a amphibolite melting garnet-free condition. We conclude here that the genera- 50 tion depth of the Taitao granitic magma must be shallower amphibolite melting than 30 km, which corresponds to the upper stability limit Post-Archaean Granite of the garnet-free field (Vielzeuf and Schmidt, 2001). (Yb)N 0 It then became ambiguous whether the source rocks 0 5 10 15 20 25 30 35 of the Taitao granitoids were subducted oceanic crust or basaltic lower crust because they have similar Fig. 8. (a) Sr/Y vs. Y diagram from Defant and Drummond geochemical compositions. The Taitao peninsula is lo- (1990). (b) [La/Yb]N/[Yb]N vs. [Yb]N diagram from Martin cated only 17 km landward from the trench, and the over- (1994). BOTH the Taitao granitoids and crustal components riding crust is expected to thin. Basaltic lower crust un- are enriched in Y and Yb, and have low [La/Yb]N and Sr/Y ra- derneath the pre-Jurassic basement must be extremely thin tios. beneath the study area, if it exists at all. The geochemical character of Taitao granitoids, which shows no typical adakitic geochemical signature, is explainable by melt- only 20 km landward from the trench. Therefore, the ing of the subducted oceanic crust. mantle wedge is most likely absent underneath the study area. This inference is inconsistent with the differentia- CONCLUSIONS tion model of a basaltic magma that originated from mantle wedge. Accretionary prism is developed in south of Intrusions of the Taitao granitoids were related both the triple junction, but not in the study area. Subduction spatially and chronologically near the subduction of the erosion of Miocene to Pliocene accretionary prism and/ Chile Ridge. Major element compositions of Taitao or Jurassic sedimentary basement might have occurred granitoids show a remarkable resemblance to those of during the ridge subduction (Bourgois et al., 1996). How- TTG suites. However, trace element compositions are not ever, few recycled zircons were recognized in the Taitao concordant with the HREE-depleted characteristics, which granitoids (Anma et al., 2009; Anma and Orihashi, 2013). are typical in Archean TTG suites. Based on trace ele- Of the possible source materials, only subducted MORB ments compositions, together with tectonic constraints, is available. According to the previous works, Sr and Nd the Taitao granitoids were inferred to have been gener- isotopic compositions of Taitao granitoids are explain- ated by melting of the subducted oceanic crust at garnet- able by 5–15% mixing of sedimentary rocks with mafic free amphibolite conditions, at depths shallower than 30 end-members of this region (Kaeding et al., 1990). Ma- km. A corollary of our results is that slab-melting-related jor source-rock of the Taitao granitoids must be magmas granitoids do not necessarily show a HREE- subducted-MORB mixed with minor amount of the sedi- depleted signature, which was used as evidence for slab- mentary components. melting for granitic rocks of the TTG suites.

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Petrogenesis of the ridge subduction-related granitoids from the Taitao Peninsula, Chile Triple Junction Area 183